Beastmaster of the Ages - Chapter 7 - Mysterious Black Arm!

A nordic romance that burns up coldly!

A teenager named Evan Mason was reincarnated into the magical world of Harry Potter and goes to school at Hogwarts!
With only his knowledge of the future and great talent for magic, he takes the path towards the top of the magic world, only to realize that ever step he took, changed everything!

- Description from Novelupdates

The days where adventurers would roam the land and grow strong are long gone. More than 99.9% of the world's population is level 1, and in fact, leveling just isn't something people think about anymore, as almost every spawn point on the planet has been gone for close to a thousand years. Only the elites, the super rich, or the super lucky have access to spawn points, and because of this, they are like Gods among men: like superheroes. For people like Zach, life is a mundane, ordinary experience of getting up, going to school, working, and then going back to bed. But that's all about to change when he stumbles upon one of the only unknown spawn points in existence. And in doing so, his life is about to descend into a wild chaos he never could have expected. (Lit RPG, fantasy, action, slow burn)

Among the demons, the supreme ones are called “Great Saints.”